The present invention relates in general to pressing molds and in particular to a new and useful method and device for compacting bulk material into railroad ties. Fine plant parts are mixed with binders in a molding press, in which moveable wall pairs that can be moved against each other form between them the filling and pressing chamber. Pressing strokes are performed alternatingly and repeatedly after which the pressed molding is cured under the effect of heat while maintaining the pressure. Such a process is known from West German Patent No. 32,27,074. In the procedure described the moveable walls are located opposite each other and define the mold chamber. The moveable walls act on the mixture entered into the mold chamber in pairs consecutively and repeatedly. This has proved successful especially in the production of I sections, whose webs and legs have approximately equal thickness.
However, if beam-shaped moldings of substantially greater cross section are to be pressed from the fine plant parts mixed with binder, as would be the case, e.g., when pressing railroad ties, the prior-art technique is not sufficient for bringing about the pressing of the fine parts over the entire cross section. Even if the outer surface of the molding to be formed is subjected to the repeated and intense action of the moveable wall pairs, the pressure that is reasonably available is not sufficient for pressing the fine parts present in the middle zone of the molding with the required intensity. What is found, instead, in this central zone of the molding is a loose structure of fine parts, which therefore fails to share the strength of the entire molding. There is even a risk of formation of shrinkage cavities or other cavities.